Apparatus and method for gasifying gas hydrate pellet

ABSTRACT

A gasification apparatus is provided which enables gas hydrate pellets to be transported and gasified in the same vessel and enables a gas to be generated by pellet decomposition in a controlled amount. The apparatus is free from bridging. The apparatus includes a heat-in-saluted vessel main body and, disposed therein, a tubular structure which is open at the top and bottom. This tubular structure holds therein gas hydrate pellets obtained by compression-molding a gas hydrate produced by the hydration reaction of a raw-material gas with raw-material water. The tubular structure becomes wider in diameter from the upper opening toward the lower opening. A channel for passing a heat carrier therethrough has been disposed between the lower end of the tubular structure and the inner bottom surface of the vessel main body. The apparatus is further equipped, between the tubular structure and the inner wall surface of the vessel main body, with a nozzle which ejects the heat carrier in a circumferential direction for the vessel main body. The vessel main body has a discharge pipe for discharging the heat carrier ejected from the nozzle, the discharge pipe projecting upright from the inner bottom surface of the vessel main body.

TECHNICAL FIELD

The present invention relates to a gasifier for carrying and gasifying agas hydrate pellet and to a method therefor.

BACKGROUND ART

Among fuel gases, particularly, natural gas (a gas mixture mainlyconsisting of methane gas, propane gas, or the like), when in a form ofliquefied natural gas, has a volume reduced down to 1/600th of that inits gaseous state. Accordingly, natural gas is transported in the formof liquefied natural gas (hereinafter, LNG) from a producing area to aconsuming area or other areas. An LNG carrier equipped with a tankcovered and surrounded by a heat-insulating material is used for thetransportation.

However, aforementioned LNG has an extremely low boiling point of −162°C., and has a characteristic that LNG rapidly evaporates as thetemperature increases. Thus, it is necessary to keep LNG under theextremely low temperature condition during transportation. For thisreason, a dedicated container having a great cold-reserving ability isrequired therefore.

In recent years, as a form of fuel gas, attention has been paid to a gashydrate that can be transported stably at a milder cooling temperaturethan that for above-described LNG. This gas hydrate is formed asfollows. Specifically, raw material gas such as natural gas and rawmaterial water are brought into gas-liquid contact at a temperature ofapproximately 0 to 5° C. under a high atmospheric pressure ofapproximately 3 to 5 MPa. Then, hydration reaction takes place to form agas hydrate. In the gas hydrate, molecules of natural gas or the likeare trapped in a lattice formed of aggregated multiple water molecules.

In order to keep a gas hydrate stable under atmospheric pressure, thegas hydrate needs to be stored at approximately −80° C. or below underequilibrium. Meanwhile, the gas hydrate has a property unique tohydrates, i.e., a so-called “self-preservation effect” that the gashydrate is relatively stable at a temperature around −20° C. which ishigher than the equilibrium temperature. Because of thisself-preservation effect, the gas hydrate has a superb characteristicthat the gas hydrate can be stored or transported over an extendedperiod under a far milder atmosphere than that for LNG, i.e., atapproximately −20° C. to −10° C. under atmospheric pressure.

Furthermore, for example, a natural gas hydrate (hereinafter, NGH), whenin a form of NGH, has a volume approximately 1/170th of that in itsgaseous form. Although having a volume reduction ratio lower than thatof LNG, NGH does not need to be kept at such an extremely lowtemperature of −162° C. as in the case of LNG. Moreover, the NGH can bestored or transported relatively stably over an extended period underatmospheric pressure. Furthermore, the NGH does not require a storagecontainer as highly durable and highly heat-insulating as that for LGN.Thus, a transport ship, cargo ship, and the like can be utilized afterbeing reconstructed for NGH transportation, saving the cost forconstructing a dedicated ship therefore, and the like.

On the other hand, a gas hydrate such as NGH is formed in a powdersnow-like form, and accordingly has problems of a low bulk density andalso a poor handling property. For this reason, as a way of decreasingthe surface area and also increasing the bulk density, such a gashydrate is compression-molded into a shape of almond, lens, sphere, orthe like. However, a gas hydrate pellet obtained by compression moldingas described above has an improved decomposition resistance. For thisreason, methods for efficiently decomposing and gasifying such a gashydrate have been proposed.

[In-Water Stirring Method]

FIG. 6 shows a scheme of a continuous introduction-type gassifier 41(see, for example, Patent Document 1). Pellets 31 are sequentiallyintroduced into a container 11 through a supply inlet 12, and broughtinto contact with water 32 whose temperature has kept at 1° C. to 5° C.to decompose the pellets for gasification. Moreover, the continuousintroduction-type gasifier 41 includes a heater 18 to maintain theaforementioned temperature by heating the water 32, since the introducedpallets 31 are normally around −25° C. to −5° C. Furthermore, a stirrer42 is provided to stir the water 32 in the container 11 to increase thecontact efficiency between the water 32 and the pellets 31 so that theheat can be rapidly transferred therebetween, and that the decompositionof the pellets 31 can be accelerated. Additionally, a discharge pipe 14is provided to maintain the water level in the container 11 at apredetermined height, since the gas hydrate includes hydration watercontained at the time of hydration reaction with raw material water andreleases the water and a gas upon decomposition.

Problems of the stirring method are that a crushing and stirring unit isneeded, and that additional power consumption is required. Moreover, forstirring, a large amount of water must be present in a space aroundpellets, and accordingly the size of the gasification tank tends to belarge.

In addition, a transfer installation is needed for transferring thepellets 31 from a storage·transportation container thereof to thegasifier 41, increasing the size of the entire gasifier 41 facility.

[Water Spraying Method]

FIG. 7 shows a gasifier 43 (see, for example, Patent Document 2.)allowing the transportation and gasification of pellets 31. In thegasifier 43, water 32 is sprayed onto the gas hydrate pellets 31 storedin a container 11.

This gasifier 43 enables the storage·transportation and gasification ofthe pellets 31 to take place in the same apparatus, making the wholeapparatus compact. Meanwhile, as the gasification proceeds, the amountof the pellets 31 filled in the container 11 is successively decreased,leading to a problem that the amount of gas generated is likely to vary.This makes it difficult to achieve stable gas supply.

Moreover, there is another problem that, even when the spraying of thewater 32 is stopped, the decomposition of the pellets 31 cannot bestopped, since the sprayed water 32 reaches all over the pellets 31filled in the container 11.

[Immersing Method]

FIG. 8 shows a gasifier 45 (see, for example, Patent Document 3.)allowing the transportation and gasification of pellets 31. The pellets31 are filled into a container 11 and transported. The pellets 31 aredecomposed by introducing water 32 into the container 11. This gasifier45 is designed so that the water 32 will be introduced from a bottomportion of the container 11. By controlling the water level in thecontainer 11, the amount of the pellets 31 immersed in the water 32 isadjusted. Furthermore, the amount of gas generated is controlled by thetemperature and the amount of water introduced.

The pellets 31 located on the bottom portion side of the container 11are immersed in the water 32, whereas the pellets 31 located at themiddle portion and top portion of the container 11 never comes intocontact with the water 32. Thereby, the amount of gas generated can beaccurately controlled by the adjustment of the water level. Thus, a gascan be supplied stably to the outside.

However, in this gasifier 45, when the pellets 31 on the bottom portionside of the container 11 are decomposed, a cavity is formed as shown inFIG. 5. As a result, there is a problem that the pellets 31 at the otherportions are not gasified due to a so-called “bridge phenomenon” inwhich the pellets 31 are not supplied downward any more.

This bridge phenomenon occurs because the pellets 31 that are in contactwith an inner wall of the container 11 adhere to the inner wall, andbecause the pellets 31 are supported at the wall surface by receiving acompression force of their own weights.

In order to eliminate a bridge 33 formed in the container 11, somecounter-measure needs to be taken such as provision of breaking meansfor physically breaking the bridge 33 in the container 11. Suchinstallation of a mechanism such as a hammer for breaking the bridge 33in the container 11 means a less loading space for the pellets 31.

Meanwhile, in a case where the breaking means is not installed in thecontainer 11, the container 11 has to be opened every time the bridge 33is to be broken. As a result, there are problems that a gas is escapedconcurrently with the opening of the container 11, and that the openingoperation is labor consuming.

-   Patent Document 1: Japanese patent application Kokai publication No.    2004-75849-   Patent Document 2: Japanese patent application Kokai publication No.    2006-160841-   Patent Document 3: Japanese patent application Kokai publication No.    2006-138349

DISCLOSURE OF THE INVENTION Problem To Be Solved By the Invention

In view of the above conventional techniques, an abject of the presentinvention is to provide a gasifier: which is capable ofcarrying·asifying a gas hydrate pellet in a single container; whichcontrols the amount of gas generated by decomposition of the pellet; andfurthermore which does not allow a bridge phenomenon to occur.

Means For Solving the Problem

A gasifier for gas hydrate pellet according to the present invention isstructured as follows.

1) The gasifier for a gas hydrate pellet according to the presentinvention is characterized by including: a container main body which isinsulated and hermetically sealed; a pellet-filling cylindrical bodyprovided inside the container main body; a nozzle through which a heatmedium for decomposing a gas hydrate pellet held in the cylindrical bodyis supplied; a gas-supply pipe through which a gas generated bydecomposition of the gas hydrate is supplied to an outside; and adischarge pipe through which the heat medium is discharged. The gasifieris characterized as follows. The pellet-filling cylindrical body has aside wall or outer wall surface formed with such a slippage angle toreduce its contact resistance with the gas hydrate pellet held therein.A disposition space for the nozzle through which the heat medium isjetted is formed between an outer wall surface of the cylindrical bodyand an inner wall surface of the container main body. A flow space forthe heat medium is formed between a lower edge of the cylindrical bodyand a bottom surface of the container main body. The heat medium isjetted in a circumferential direction of the disposition space for thenozzle.

2) The gasifier is characterized as follows. Friction reducing means forreducing the contact resistance with the pellet is formed on an innerwall surface of the cylindrical body holding the gas hydrate pellet. Thefriction reducing means is any of a plurality of protruding stripsextending vertically, a plurality of convexes and concaves, and apolytetrafluoroethylene resin coating film.

3) The gasifier is characterized as follows. The discharge pipe for theheat medium provided in the bottom surface on an inner side of thecontainer main body includes a discharge outlet formed at a tip end ofthe discharge pipe, the discharge outlet being for discharging the heatmedium. The discharge pipe is provided in a manner that the tip endthereof is vertically movable.

4) The gasifier is characterized in that the container main body isformed so as to be capable of cargo transportation.

Moreover, a gasifying method for a gas hydrate pellet according to thepresent invention is structured as follows.

5) The method is characterized by including the steps of: jetting a heatmedium for decomposing a gas hydrate pellet in a circumferentialdirection of the inner wall surface of the container main body; forminga swirl flow of the heat medium on a bottom surface side of thecontainer main body by the heat medium thus jetted; and bringing theheat medium into contact with the gas hydrate pellet by the swirl flowfor decomposition.

6) The method is characterized in that a decomposition speed of the gashydrate pellet is adjusted by adjusting a liquid surface height of theheat medium reserved on the bottom surface side of the container mainbody.

Effects of the Invention

1) A cylindrical main body 15 is provided inside a container 11 forcarrying gas hydrate pellets, the cylindrical main body 15 having areverse-tapering form, that is, its diameter gradually increases towardthe bottom. This makes it hard to transmit a compression force to thepellets 31, and eliminates the formation of a bridge 33.

As a result, the gas hydrate pellets are stably supplied to a lowerportion of the container 11, stabilizing the gasification and achievingstable gas supply to the outside.

2) Moreover, a stripe body is formed on the inner wall surface of thecylindrical body 15. Thereby, the pellets 31 that are in contact withthe inner wall surface are prevented from being adhered to the innerwall surface. Furthermore, the inner wall surface of the cylindricalbody 15 is covered by polytetrafluoroethylene. Thereby, the adhesion isfurther prevented, eliminating the formation of the bridge 33.

3) When water 32 is supplied into the container 11, the water 32 issupplied through a nozzle 19 provided at the lower portion of thecontainer 11. Accordingly, a swirl flow 22 of the water 32 is formedinside the container 11. This swirl flow improves the contact efficiencybetween the pellets 31 and the water 32, and thereby the gasification isconducted efficiently. Furthermore, by immersing the pellets 31, afilled condition is created. The water 32 flows through pellet pores,and the apparent flow rate is increased, providing a higher heattransfer effect.

Additionally, the swirl flow 22 makes the temperature of the water 32uniform, preventing the pellets 31 from being decomposed locally.

4) The nozzle 19 through which a heat medium 32 for decomposing thepellets 31 is provided in a nozzle installation space A between thecontainer main body 11 and the pellet-filling cylindrical body 15, theheat medium 32 being jetted in the circumferential direction of thecontainer main body 11. Thereby, the clogging of the nozzle 19 at thetip end side by the pellet 31 is prevented, and the immediate collisionof the jetted heat medium 32 with the pellet 31 is also prevented.Accordingly, the preferable swirl flow 22 can be formed.

5) The water 32 is discharged from the container 11. This dischargedwater is heated and then returned to the container 11 again for cyclicutilization. Thus, a gasifier 10 alone can supply a gas withoutadditional fresh water from the outside.

More specifically, simply loading the gasifier 10 on transportationmeans such as a truck and connecting a gas-supply pipe 13 of thegasifier 10 to a gas-supply installation enables the gas to be supplied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram (cross-sectional view) of agasifier for a gas hydrate pellet according to the present invention.

FIG. 2 is a schematic configuration diagram (horizontal cross-sectionalview) of the gasifier for a gas hydrate pellet according to the presentinvention.

FIG. 3 is a drawing showing one example of a stripe body on acylindrical body.

FIG. 4 is a drawing showing a state where a hydrate is decomposed when aswirl flow is not present.

FIG. 5 is a schematic diagram of a bridge.

FIG. 6 is a schematic diagram of a conventional gasifier (in-waterstirring method).

FIG. 7 is a schematic diagram of a conventional gasifier (water sprayingmethod).

FIG. 8 is a schematic diagram of a conventional gasifier (immersingmethod).

FIG. 9 is a drawing showing a transportation form of the gasifier for agas hydrate pellet according to the present invention.

EXPLANATION OF REFERENCE SYMBOLS

-   10 Gasifier-   11 Container-   12 Supply inlet-   13 Gas-discharge pipe-   14 Discharge pipe-   15 Cylindrical body-   16 Gas-liquid separator-   17 Reservoir tank-   18 Heater-   19 Nozzle-   21 Water flow-   22 Swirl flow-   23 Stripe body-   31 Pellet-   32 Water

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, description will be given of a gasifier for a gas hydratepellet according to the present invention with the drawing.

Embodiment 1

As shown in FIG. 1, gasifier 10 for a gas hydrate pellet according tothe present invention includes a cylindrical body 15 disposed in acontainer 11. The cylindrical body 15 has a tapering form, so that itsdiameter gradually increases toward the bottom. Gas hydrate pellets 31introduced through a supply inlet 12 at the upper portion of thecontainer 11 are stored inside the cylindrical body 15. This cylindricalbody 15 is made of a metal such as aluminum and stainless steel or madeof a resin. The inner wall surface of the cylindrical body 15, whichcomes into contact with the pellets 31, is embossed so as to reduce thecontact resistance with the pellets 31.

At a lower portion of the container 11, multiple nozzles 19 are providedto jet water 32. The water 32 is jetted through these nozzles 19 in thesame circumferential direction, and the water 32 is swirled in thecontainer 11. Moreover, a discharge pipe 14 is provided upright at thecenter of the bottom portion of the container 11 so as to discharge thewater 32 in the container 11. The water 32 thus discharged flows into areservoir tank 17 equipped with a heater 18. The water 32 is heated bythe heater 18, and then jetted again into the container 11 through thenozzles 19 via a pump 35.

A gas-discharge pipe 13 is provided in an upper portion of the container11 to discharge a gas outside the apparatus, the gas being generated bydecomposition of the pellets 31. A gas-liquid separator 16 is providedto the gas-discharge pipe 13. This gas-liquid separator 16 separateswater in the gas from the gas. The water is returned to the reservoirtank 17, while the gas is supplied to an external installation such as asupply installation.

In FIG. 1, the nozzles 19 are installed in a nozzle installation space Aformed between the container 11 and the cylindrical body 15 so as toform a swirl flow 22 without disturbing the flow of the water 32 jettedfrom the nozzles 19. To put it differently, this prevents the flowdisturbance of the jetted water 32 due to the contact of the pellet 31with the tip end of the nozzle 19. Moreover, a flow space B is formed,where the water 32 thus jetted flows swiftly toward the bottom surfaceof the container 11.

In the gasifier 10 thus structured for the gas hydrate pellets 31, thepellets 31 produced by a pellet production installation are introducedinto the container 11 through the supply inlet 12. The container 11filled with the pellets 31 is loaded on carrying means carried to a gassupply installation.

In the gasifier 10 carried to a destination, for example, the water 32heated at 1° C. to 5° C. by the heater 18 is pressure-pumped by the pump35 and jetted into the container 11 through the nozzles 19. By the jetflow of the water 32 thus jetted, the swirl flow 32 of the water 32 isformed in the container 11 as shown in FIG. 2, and the pellets 31 aredecomposed. The water 32 is discharged through the discharge pipe 14provided upright at the bottom portion of the container 11, and flowsinto the reservoir tank 17. As shown in FIG. 2, the water 21 is jettedthrough the multiple nozzles 19 in the same circumferential direction,and this jet flow forms the swirl flow 22. The swirl flow 22 makes thetemperature distribution of the water 32 uniform.

Moreover, for example, when the swirl flow 22 is not present, some ofthe pellets 31 remain unmelted and are shaped into columnar forms asshown in FIG. 4, which causes a bridge 33 to be formed in some cases. Byforming the swirl flow 22, in contrast, such an incident is prevented.FIG. 4 shows the unmelted pellets 31 when the multiple nozzles 19 areprovided toward the center of the container 11.

The gas generated by decomposition of the pellets 31 is supplied to theexternal supply installation or the like through the gas-discharge pipe13. Water generated by decomposition of the pellets 31 is dischargedthrough the discharge pipe 14 to the reservoir tank 17 for reuse.

Embodiment 2

In a gasifier 10 of this embodiment, a stripe body 23 as shown in FIG. 3is formed on the inner wall of a cylindrical body 15. The stripe body 23further prevents adhesion between the pellets 31 and the inner wall ofthe cylindrical body 15. The inner wall of the cylindrical body 15 maybe covered by polytetrafluoroethylene in addition to the stripe body 23.Alternatively, a waved plate such as a corrugated plate can be used asthe inner wall of the cylindrical body 15.

Embodiment 3

In this embodiment, a gasifier 10 is loaded on a truck 36 as shown inFIG. 9, allowing the transfer to a place where the gas supply is needed.For example, the gasifier 10 is transferred to a disaster area or anisolated island by the truck 36. A gas-supply pipe 24 is connected toequipment or the like that uses the gas as its fuel. Thus, the gassupply is achieved.

In the gasifier 10, a single container 11 serves as both a carryingcontainer and a gasification container. Thus, gasification is conductedfreely at the carrying destination for the gas supply.

The present invention provides a gasifier: which is capable ofcarrying·gasifying a gas hydrate pellet in a single container; whichcontrols the amount of gas generated by decomposition of the pellet; andfurthermore which does not allow a bridge phenomenon to occur.

INDUSTRIAL APPLICABILITY

A gasifier and gasifying method for a gas hydrate pellet according tothe present invention provide a gasifier and a gasifying method whichare capable of carrying·gasifying a gas hydrate pellet in a singlecontainer; which controls the amount of gas generated by decompositionof the pellet; and furthermore which does not allow a bridge phenomenonto occur. Thereby, stable gas supply from the gas hydrate pellet isachieved, and gasification can be conducted freely at a carryingdestination for the gas supply.

1. A gasifier for a gas hydrate pellet characterized by comprising: acontainer main body which is insulated and hermetically sealed; apellet-filling cylindrical body provided inside the container main body;a nozzle through which a heat medium for decomposing a gas hydratepellet held in the cylindrical body is supplied; a gas-supply pipethrough which a gas generated by decomposition of the gas hydrate issupplied to an outside; and a discharge pipe through which the heatmedium is discharged, the gasifier characterized in that thepellet-filling cylindrical body has a side wall formed with such aslippage angle to reduce its contact resistance with the gas hydratepellet held therein, a disposition space for the nozzle through whichthe heat medium is jetted is formed between an outer wall surface of thecylindrical body and an inner wall surface of the container main body, aflow space for the heat medium is formed between a lower edge of thecylindrical body and a bottom surface of the container main body, andthe heat medium is jetted in a circumferential direction of thedisposition space for the nozzle.
 2. The gasifier for a gas hydratepellet according to claim 1, characterized in that friction reducingmeans for reducing the contact resistance with the pellet is formed onan inner wall surface of the cylindrical body holding the gas hydratepellet, and the friction reducing means is any of a plurality ofprotruding strips extending vertically, a plurality of convexes andconcaves, and a resin coating film.
 3. The gasifier for a gas hydratepellet according to claim 1, characterized in that the discharge pipefor the heat medium provided in the bottom surface on an inner side ofthe container main body includes a discharge outlet formed at a tip endof the discharge pipe, the discharge outlet being for discharging theheat medium, and the discharge pipe is provided in a manner that the tipend thereof is vertically movable.
 4. The gasifier for a gas hydratepellet according to claim 1, characterized in that the container mainbody is formed so as to be capable of cargo transportation.
 5. Agasifying method for the gasifier for a gas hydrate pellet according toclaim 1, the method characterized by comprising the steps of: jetting aheat medium for decomposing a gas hydrate pellet in a circumferentialdirection of the inner wall surface of the container main body; forminga swirl flow of the heat medium on a bottom surface side of thecontainer main body by the heat medium thus jetted; and bringing theheat medium into contact with the gas hydrate pellet by the swirl flowfor decomposition.
 6. The gasifying method for the gasifier for a gashydrate pellet according to claim 5, characterized in that adecomposition speed of the gas hydrate pellet is adjusted by adjusting aliquid surface height of the heat medium reserved on the bottom surfaceside of the container main body.